Avaya, Motorola and Proxim this week are expected to announce a co-developed handset and enterprise network gear that let mobile phone users roam between cellular networks and wireless LANs.

The combination holds the promise of cutting phone costs for business customers and making mobile workers more productive. It is based on a new Session Initiation Protocol (SIP)-based Wi-Fi/cellular handset from Avaya and Motorola, IP-based or IP-enabled PBXs from Avaya, plus new WLAN switch and thin access points developed by Avaya and Proxim.

Users are both intrigued and skeptical.

"We have hundreds of house staff who need internal wireless communication at low cost," says John Halamka, CIO at CareGroup Systems, a Boston hospital network. With an Avaya PBX network, Halamka says he is looking into the vendor's Extension to Cellular technology, which lets any cell phone act as an extension of a PBX. But further integration of cellular and WLAN would be more valuable, he says, because staff could use their cell phones for five-digit dialing over CareGroup's WLAN. This also would reduce the electromagnetic interference that signals from cell phones cause.

Another user points to a potential drawback in the cellular/voice-over-WLAN (VoWLAN) technology.

"The gotcha is that you have to use the Avaya [access point]," says David Donoho, senior telecommunications network engineer at the University of Maryland in College Park. "We just put in a bunch of Cisco 802.11 [access points], and there's no way we're going to pull all those out just to [deploy cellular and VoWLAN roaming capabilities]."

The university, which has a mixed IP/TDM Avaya phone network, uses the vendor's Extension to Cellular feature. Donoho adds that another issue with the cellular/VoWLAN technology is that only Motorola phones initially would work on the network.

Analysts say the combination of cellular and WLAN technologies will appeal to large companies with many mobile phone users who often rack up big cell phone bills because they use their mobile phones while in the office.

"Companies that deploy Wi-Fi networks will soon find out that the incremental costs of adding voice is not that much," says Philip Solis, senior analyst with ABI Research. Giving only one device to employees - instead of a cell phone and desktop phone - could be another cost-saving measure. Letting employees have one voice mail box and one phone number also could make workers more productive, he adds.

Team effort

Avaya, Motorola and Proxim announced their partnership last year. One of the main components of the jointly developed product package - dubbed Seamless Mobility - is a Windows-CE-based Motorola phone, which includes 802.11a and cellular radios. The device lets users inside an office make calls from an Avaya IP PBX and Wi-Fi-enabled VoIP network.

Mobile users calling an extension in an office also can roam between their corporate WLANs and cellular networks and have the calls handed off without interruption, Avaya says. Future versions of Seamless Mobility will let users connected to any phone on any network roam between networks without dropping calls, Avaya says.

Software on the phone, written by Motorola and Avaya, lets users dial extension numbers when in an office, as well as access all Avaya PBX features. A SIP stack on the phone supports a push-to-talk feature for connecting to co-workers with SIP-based devices. The software also senses for the presence of Wi-Fi and cellular signals; priority is placed on putting external calls over a Wi-Fi signal because the toll cost of a call made on a PBX generally would be less than a cell phone network charge. If Wi-Fi is unavailable, the phone calls the cellular network.